This invention relates generally to switching amplifiers and, in particular, to a method and apparatus for detecting the specific load impedance being driven by an inductive boost amplifier and using that information to modify amplifier perfromance.
Switching amplifiers, by their nature, usually introduce undesirable switching frequency components at their outputs unless low pass filters are employed. These filters are usually passive designs, sensitive to the load impedance being driven. As it is not always possible to predict the exact load impedance that an amplifier will ultimately statically or dynamically drive, the possibility exists that the actual load impedance will deviate significantly from that assumed in the design.
The resultant filter mismatch results therefore in poor amplifier performance. Furthermore, timing relationships based on load impedance in an inductive boost amplifier are compromised by load variances, resulting in distortion products. A need therefore exists for a mechanism to allow acceptable switching amplifier performance over a range of load impedances.
The present invention resides in a method and associated apparatus for detecting the specific load impedance being driven by an inductive boost amplifier, and using that information to modify amplifier operation.
Various load impedances may be connected to the improved amplifier while accommodating the impedance of different amplifier loads subject to change under various conditions such as temperature, voltage, frequency, etc. Thus, in addition to compensation of static load impedance variances, the present invention is quite effective in compensating for dynamic variances as well.
Although the description focuses on variable load impedance compensation, it is anticipated that simpler implementations of the technique may be used to selectively switch output filter components into operation in response to specific load impedance ranges, yielding a similar, albeit coarser, net result. The invention may be used as well to regulate other amplifier functions, such as back-EMF shunt timing, and other circuits.